Photographic emulsions



Patented Aug. 23, 1938 UNITED STATES PHOTOGRAPHIC EMULSFONS Stand and Joseph L. Connolly, Roches assignors to Eastman Kodak O Cyril J.

ter, N. Y.,

pany, Jersey City, J., a

Jersey No Drawing.

omcorporation of New Application April 16, 1936,

Serial No. 74,814

10 Claims.

This invention relates to photographic emulsions and particularly to photographic emulsions in which a cellulosic compound is substituted for a part or all of the gelatin used to disperse the light sensitive salt.

It is customary to make photographic emulsions by dispersing a silver halide in a solution of gelatin, the gelatin serving as a protective colloid to keep the silver halide in suspension. The use of other materials for this purpose in place of gelatin has been suggested. Among such materials are collodion, regenerated cellulose and water-insoluble cellulose esters, such as cellulose acetate. None of these compounds, however, has the unique chemical and physical properties of gelatin which make it especially suitable for photographic emulsions. 0n the other hand, gelatin has several disadvantages among which are the difficulty of obtaining uniformity in its preparation and its solubility at high temperatures which makes its use objectionable in photographic emulsions to be processed in warm climates.

It is, accordingly, an object of the present invention to provide a photographic emulsion in which a part or all of the gelatin has been substituted by a cellulosic compound. A further object is to provide a method for inducing gel formation of the cellulosic compounds used. Other objects will appear from the following description of. our invention.

These objects are accomplished by preparing a gelatin emulsion and adding to it a suitable amount of solution of a water-soluble cellulose carboxylic acid ester, such as water-soluble acid esters of cellulose with polycarboxylic acids, alkali and other water-soluble metal salts and a1- kyl esters of these compounds, and hydroxy monocarboxylic acid esters of cellulose.

In making an emulsion, according to our invention, an ordinary gelatin emulsion is first made according to any well-known method. To this emulsion is added a water solution of'a suitable r water-soluble cellulosic compound which has been treated, if necessary, with a salt which induces gel formation. The resulting solution is coated on a support and dried or is set and shredded for later use in any well-known manner.

In making an emulsion of a mixture of gelatin and a cellulosic compound in this way, the proportion of gelatin andthe cellulosic compound may vary over a wide range. We have found that emulsions may be produced in which thela proportion of gelatin ranges from 100% down to 20% and the proportion of cellulosic compound may be any amount up to 80%. i

It is also possible to form a dispersion in which the cellulosic compound constitutes the whole of the protective colloid. According to this method of procedure, the gelatin emulsion, after formation in the usual way, is diluted with-water and centrifuged for several minutes. This throws the silver halide grains to the bottom of the tube and the supernatant liquid can then be decanted and removed. If water at approximately 45 C. is then added and the centrifuging continued and this process repeated two or three times, the silver halide grains may be obtained reasonably free of gelatin. To the grains there is then added asuitable quantity of a cellulosic ester, such as cellulose acetate phthalate triethanolamine salt and the material is stirred. The silver halide grains are in this way dispersed in the cellulosic compound to form the emulsion, which may then be coated in the normal way.

The following examples, which are by way of illustration only, are methods of forming emulsions according to our invention:

Example 1.-To cc. of a gelatino-silver halide emulsion formed in the usual way'there were added 20 cc. of a 5% aqueous solution of cellulose acetate lactate. The resulting emulsion was stirred and coated onto glass plates immediately. The plates were dried and were then 3 exposed and developed in the usual way. The emulsion was found to have satisfactory photographic properties and did not exhibit objectionable fogging or desensitization.

Example 2.-To 200- cc. of a gelatino-silver halide emulsion made in the usual way, there were added 200 cc. of a 5% solution of cellulose acetate phthalatepotassium salt. The resulting mixture was thoroughly stirred and coatedonto glass plates at once. The plates were dried and were exposed in a sensitometer. Samples of the plates were then developed for lengths of time varying from 30 seconds to 16 minutes. On comparing plates formed in this way with 'plates formed by mixing 200 cc. of the photographic emulsion with 20 cc. of a 6% gelatin solution, dried, exposed and developed in the same way, it was found that at the end of four minutes development the emulsion containing a cellulose derivative had a gamma of 1.58, whereas the emulsion containing only gelatin showed a value for gamma of 1.2. The cellulose derivative did not exhibit objectionable fogging or desensitization,

Among the compounds which are suitable for use in emulsions according to our invention, there are included water-soluble polycarboxylic acid esters of cellulose, such as cellulose acid phthalate, cellulose acid succinate and cellulose citrate; mixed esters containing a polycarboxylic acid radical, such as cellulose acetate phthalate; and

water-soluble salts and esters of these compounds, such as cellulose potassium phthalate and cellulose acetate methyl phthalate. These acid esters of cellulose and their water-soluble salts, and a method for their preparation are described in 'Malm and Waring U. S. Patent No. 2,093,462, granted September 21, 1937. The general method of producing them is to treat a cellulosic material, such as cellulose or cellulose acetate with a polycarboxylic acid anhydride, such as phthalic anhydride in the presence of an organic base, such as pyridine, quinoline, or the like. The resulting product in that case is then washed with dilute acid to remove substantially all of the pyridine or other base and to give a polycarboxylic acid ester of cellulose in which each of the polycarboxylic acid radicals presents a free unesterified carboxylic group. This group may then be treated with an alkali metal-hydroxide or an alcohol to produce an alkali salt or an ester.

Anothertype of polycarboxylic acid ester which may be used according to our invention is that formed by reacting an ethanolamine with an acid polycarboxylic acid ester of cellulose. Compounds of this type are cellulose phthalate triethanolamine salt, the production of which is described in Fo-rdyce U. S. Patent No. 1,969,741,

granted August 14, 1934.

Still another type of compound, the alkali metal salts of which may be used according to our invention, is the group of heterogenously linke dicarboxylic acid esters of cellulose, such as cellulose dilactate, cellulose diglycollate, cellulose acetate diglycollate, etc. The compounds are described in Malm and Fordyce U. S. Patent No.- 2,024,238, granted December 17, 1935.

We may also use as protective colloids for the sensitive silver salt, hydroxy-monocarboxylic acid esters of cellulose. Compounds of this class are cellulose acetate glycollate, cellulose acetate hydracrylate, cellulose acetate lactate, cellulose acetate propionate glycollate and cellulose acetate propionate lactate. Compounds of this class are desscribed in Staud and Webber U. S. Patent No. 1,957,856, granted May 8, 1934.

Any water-soluble alkali salts of these compounds may be used although we have found the potassium and ammonium salts particularly useful. The alkaline earth metal salts, such as calcium or any of the metals which form insoluble salts of the acid esters of cellulose are unsuitable for the purposes of our invention. The watersolubilities of these cellulose compounds depend in large measure upon the ionization of the metal atom orother group attached to the free carboxyl of th polycarbdxylic acid. The proportion of these solubilizing groups in the molecule is, therefore, of importance in determining the watersolubility of the cellulose compound-used.

In using these cellulosic compounds in admixture with gelatin it is sometimes necessary to add to them compounds which induce gel formation, in order that a gel may be produced which is similar to that produced by the setting of gelatin solutions.

We have found that if 5 cc. of a 10% solution of cupric acetate was added to 10 cc. of a 10% aqueous solution of cellulose acetate phthalate triethanolamine salt a. stifl gel was produced which was not readily soluble in warm water.

When 15 cc. of a 10% solution of sodium chloride was added to 10 cc. of 10% solution of cellulose acetate phthalate triethanolamine salt, gel formation was also obtained.

On the addition of 5 cc. of 5% solution of cerous sulfate to 10 cc. of the 10% solution of celluloseacetate phthalate triethanolamine salt, salts were precipitated in flake formation.

A 10% aqueous solution of cellulose acetate phthalate potassium salt was made up and to 10 cc. of this solution there were added various amounts of a 2%% solution of chrome alum. When 2% cc. of this chrome alum solution were added, a gel was produced in about one-quarter of an hour. When 3 cc. of chrome alum solution were added to a similar solution of the cellulosic compound, the time of setting was found to be decreased. When 4 cc. of the chrome alum solution were added, the viscosity of the solution at 50 C. was found to be fairly low and upon chilling to 15 C., or lower, the solution set to a gel immediately.

It is apparent that relatively small amounts of these inorganic salts serve to induce gel forma tion of the cellulose compounds and the small amounts of the salts used do not adversely aiiect the photographic sensitivity of the emulsion with which the cellulosic compounds are mixed.

A method for forming a dispersion of silver halides in water soluble cellulosic compounds, such as those described in the present application, is also disclosed in Sheppard and Houck U. S. application Serial No. 74,817, filed April 16, 1936.

It is to be understood that other compounds and other methods of procedure than those included in the above description of our invention may be used and that our invention is to be limited only by the scope of the appended claims.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A photographic emulsion containing a silver halide dispersed in an appreciable amount of a water soluble cellulose ester selected from the group consisting of polycarboxylic acid esters oi cellulose and hydroxy-monocarboxylic acid esters of cellulose.

2. A photographic emulsion containing a silver halide dispersed in a substantially equal mixture of gelatin and a water soluble cellulose ester selected from the group consisting of polycarboxylic acid esters of cellulose and hydroxy-monocarboxylic acid esters of cellulose.

3. A photographic emulsion comprising a silver halide dispersed in a substantially equal mixture of gelatine and cellulose acetate lactate.

4. The method of making a sensitive photographic emulsion which comprises dispersing a silver halide in gelatin and dispersing therein an appreciable amount of a water soluble cellulose ester selected from the group consisting of polycarboxylic acid esters of cellulose and hydroxymonocarboxylic acid esters of cellulose in an appreciable amount but less than that at which the gelatin and cellulose ester are incompatible.

5. The method of making a sensitive photographic emulsion which comprises dispersing a silver halide in gelatin and dispersing therein a water soluble polycarboxylic acid ester of cellulose in an appreciable amount but less than that at which the gelatin and the cellulose ester are incompatible.

6. The method of making a sensitive photoan amount about equal to the amount of gelatin.

graphic emulsion which comprises dispersing a silver halide in gelatin and dispersing therein an alkali metal salt of a polycarboxylic acid ester of cellulose in an appreciable amount but less than that at which the gelatin and the celluose ester are incompatible.

'7. The method of making a sensitive photographic emulsion which comprises dispersing a silver halide in gelatin'and dispersing therein a hydroxy-monocarboxylic acid ester of cellulose in an appreciable amount but less than that at which the gelatin and the cellulose ester are in.- compatible. I

8. The method of making a sensitive photo graphic emulsion which comprises dispersing a silver halide in gelatin and dispersing therein cellulose acetate phthalate triethanolamine salt containing sodium chloride about equal in amount to the cellulosic compound, the cellulose acetate phthalate triethanolamine salt being present in 9. The method of making a sensitive photographic emulsion which comprises dispersing a silver halide in gelatin and dispersing, therein cellulose acetate phthalate potassium salt containing from one-half to an equal amount of chrome alum, the cellulose acetate phthalate potassium salt being present in an amount about equal to the amount oi. gelatin.

10. A photographic emulsion containing a silver halide dispersed in an appreciable amount of a substantially water-soluble compound selected from the group consisting of cellulose esters of hydroxy-monocarboxylic acids, alkali metal salts of polycarboxylic acid esters of cellulose, and alkyl esters of polycarboxylic acid esters of cellulose.

CYRIL J; STAU'D.

JOSEPH L. CONN'ELLY. 

